Conventionally known clasps provided to both ends of accessories used in the form of a ring such as a necklace, a bracelet, and an anklet are described in Patent Documents 1 and 2. Patent Document 1 describes a coupling part for self-locking accessory including a pair of a concave portion and a convex portion that each include magnets so that the concave portion and the convex portion are attracted to each other in the direction of the long axis by magnetic attraction force, the concave portion including a pin in the inner side, the convex portion including an edge on the upper outer surface that is arranged to be engaged with the pin.
Patent Document 2 discloses a clasp for accessories that includes a first coupling body including a concave portion for insertion and a second coupling body including an insertion portion that is insertable into the concave portion for insertion, and has a configuration such that attraction force is generated by magnetic attraction force between the first coupling body and the second coupling body. A spiral convex portion including a retaining surface making up a retaining concave portion and a guiding surface is provided to the first coupling body on the inner peripheral surface of the concave portion for insertion of the first coupling body, and a retaining convex portion arranged to move along the guiding surface of the spiral convex portion and can be locked in the state of being inserted into the retaining concave portion is provided to the insertion portion of the second coupling body.